Occurrence, Symptom Expression and Characterization of Phytoplasma Associated with Pear Decline Disease in Catalonia (Spain)

A total area of 1500 ha of commercial plots was surveyed to study the extent of pear decline disease and its relative importance in northeastern Spain. A preliminary evaluation indicated that around 7% of the plots had symptoms of the disease. At the same time, pear decline incidence was evaluated in 45 plots, by visual inspection of 500 trees in each plot. In September, the incidence of trees with symptoms ranged from 8 to 59% depending on the cultivar selected. The presence of pear decline (PD) phytoplasma in these plots was confirmed by polymerase chain reaction (PCR) amplification of phytoplasma DNA with universal or group-specific primers. Restriction fragment length polymorphism analyses also showed the presence of a unique phytoplasma strain. The symptom expression of PD disease in different cultivars was evaluated throughout the year. The relationship between the presence of symptoms and detection of PD by PCR in these cultivars was also studied. Results showed that the nested- PCR, using specific primers to detect the DNA from PD phytoplasma, is the most accurate method to identify the total percentage of affected trees